US researchers in a study published in the Archives of General Psychiatry have said that measuring levels of a hormone half way through pregnancy can predict if the woman will be at risk of post natal depression. The hormone in question here is corticotropin-releasing hormone (CRH), which is produced by the placenta and involved in regulating many other hormones. Increased levels of this hormone can indicate the women who are likely candidates for postpartum depression.

Postnatal depression affects 10-15% of mothers and usually starts within four to six weeks of giving birth. A history of depression, stressful life events, a lack of social support, low self-esteem, anxiety or stress during pregnancy are all said to be known risk factors.

In their report Dr. Ilona S. Yim at the University of California, Irvine, and co-investigators said, "The high incidence and severe consequences of postpartum depression make the identification of women at risk an important research goal."

The researchers conducted a study on 100 women in which hormone levels in the blood were measured at 15, 19, 25, 31 and 37 weeks' of pregnancy. The last four pregnancy visits again the CRH levels were measured as well as at an average of 8.7 weeks after giving birth.

16 women developed post natal depression and the researchers found that increased levels of the hormone CRH at 25 weeks helped predict as many as three quarter of the women who developed postpartum blues. This association remained at a significant level even after depression in the early stages of pregnancy was taken into account.

If the result were proven in larger studies the researchers felt this could become a routine test for depression during pregnancy. If women are assessed mid pregnancy the results of placental CRH are enhanced.  The researchers said, "Because blood draws to screen for gestational diabetes are typically performed at 24 to 28 weeks gestational age, a potential postpartum depression screen could be completed at the same time."

The researchers said during pregnancy levels of the hormone increase which in turn increases the production of cortisol, which helps the body deal with stress. After birth the levels of placental CRH drop considerably which in turn lead to a decrease in cortisol. The women who have higher levels of placental CRH face a more dramatic dip.

Dr Yim said, "If our results are replicable, it may be considered useful to implement a pCRH postpartum depression screen into standard prenatal care.”

Dr Patrick O'Brien, spokesman for the Royal College of Obstetricians and Gynecologists, said, "The thing with postpartum depression is that once it is identified it usually can be treated very well. But the problem is that often women withdraw within themselves and don't seek help. If the test was proved to work, then you could increase surveillance of those at risk." (Harkiran contributed to this report)